It is well known to correct the position of a portion of a vertebral column, or to immobilize such a portion, using vertebral osteosynthesis equipment comprising rigid connecting bars, capable of connecting several vertebrae, bone anchoring members, capable of being anchored in the vertebrae, and connecting parts making it possible to rigidly connect the connecting bars to said bone anchoring members so as to anchor said connecting bars to the vertebrae.
The use of such equipment is, however, problematic when the patient is a child or adolescent, the equipment not being able to adapt itself to the growth of the patient and requiring periodic repeat surgical operations to adapt the position of the connecting parts relative to the connecting bars.
To try to resolve this problem, percutaneously maneuverable systems have been designed. The systems are, however, complex and not fully satisfactory.
Furthermore, the publication of American patent application Nr. US 2011/270314 A1 describes equipment comprising:                at least one rigid connecting bar, capable of connecting several vertebrae,        first bone anchoring members and first connecting parts, capable of anchoring the connecting bar to the vertebrae with immobilization of that bar relative to the first connecting parts, and        second bone anchoring members secured to second connecting parts capable of anchoring the connecting bar to the vertebrae with sliding of the bar relative to the second connecting parts; each of these two bone anchoring members is formed by a screw body and each of these two connecting parts comprises a receiving conduit through which the bar is received slidingly and includes a contact member therein forming a contact interface between said second connecting part and said bar.        
In the applicant's opinion, this equipment may be problematic in terms of the complexity of placement and rapid wear of said contact members. Furthermore, a risk of blocking the sliding of the bar relative to said second connecting parts, following the growth of bone cells around said bar and said second connecting parts, cannot be ruled out, thereby making the equipment ineffective.